This invention relates to the production of glass fibers, e.g., fibers made by melting particulate batch ingredients or minerals, including basalt and the like, and, more particularly, to an arc furnace for producing such glass fibers.
Prior art arc furnaces, such as that disclosed in Slayter et al., U.S. Pat. No. 2,280,101, employ side entering electrodes to complete the electric circuit of the arc electrode. It has been found that the side entering electrodes cause hot spots in the sidewall refractory and also cause such refractory to erode quickly. The temperatures in an arc furnace are greatest at the glass-batch interface and, consequently, refractory wear is also greatest at the melter sidewalls near the glass-batch interface. In the prior art the sidewalls have been constructed of a high resistance refractory material, such as fused cast alumina and zirconia, which does not have the wear properties that are exhibited by low resistance refractory material, such as chromic oxide. The high resistance refractory material has been utilized in the prior art arc furnaces to prevent electrical short circuiting through the melter sidewall refractory. However, such refractories have been unacceptable since they tend to wear rather rapidly. Another problem encountered in arc furnaces with side entering electrodes is the impossibility of restarting the arc if the glass level in the melter drops below the side electrodes.
In prior art arc furnaces, such as that disclosed in Eimer, U.S. Pat. No. 1,438,936, a single bottom entering electrode has been employed to complete the electric circuit for the arc electrode. However, it has been found that such furnaces tend to produce a hot spot or streak through the center of the furnace between the arc electrode and the bottom entering electrode. This hot streak through the center of the furnace provides an unbalanced temperature distribution and hence limited control of the temperature of the glass exiting from the furnace.
Therefore, it is an object of the present invention to provide an arc furnace for melting glass that minimizes the sidewall refractory wear, minimizes hot spots in both the sidewall refractory and in the molten glass itself, and provides a uniform temperature distribution and good exit temperature control.